Electroless codeposition of nickel alloys

ABSTRACT

THE INVENTION RELATES TO A METHOD FOR ELECTROLESSLY DEPOSITING A NICKEL-TIN ALLOY LAYER AND FOR DEPOSITING A NICKEL-MOLYBDENUM ALLOY LAYER AND TO BATHS THEREFOR. THE ELECTROLESS PLATING BATH FOR NI-SN COMPRISES AN AQUEOUS SOLUTION CONTAINING NICKEL IONS, STANNATE IONS, SODIUM TARTRATE, SODIUM HYPOPHOSPHITE, GLYCINE AND SUFFICIENT KOH TO BRING THE BATH TO A PH OF ABOUT 13.5. THE ELECTROLESS PLATING BATH FOR NI-MO COMPRISES AN AQUEOUS SOLUTION CONTAINING NI IONS, GLYCINE, SODIUM HYPOPHOSPHITE, MOLYBDATE IONS, AND KOH TO BRING THE PH TO ABOUT 13.5.

United States Patent ()1 ice 3,674,516 Patented July 4, 1972 3,674,516 ELECTROLESS CODEPOSITION F NICKEL ALLOYS Zlata Kovac, 5 Bayard Road, Apt. 913, Pittsburgh, Pa. 15213 No Drawing. Filed Nov. 27, 1970, Ser. No. 93,444 Int. Cl. C23c 3/02 U.S. Cl. 106-1 14 Claims ABSTRACT OF THE DISCLOSURE BACKGROUND OF THE INVENTION Nickel films are used for electromagnetic shielding coatings on electrical equipment. Nickel is used to provide an electrical shielding effect because of its ferro-magnetic property. It is desired in electromagnetic coatings for shielding purposes that the nickel coating have the following properties: relatively high solid solderability, corrosion resistance, chemical resistance, mechanical resistance and relatively low electrical contact resistance. The present day nickel coatings are somewhat deficient in the above properties. It is known theoretrically that the addition of a significant percentage of tin to a coating of nickel should improve the above properties. Further, addition of molybdenum to nickel is also known to improve its corrosion resistance property. However, prior art attempts to deposit nickel-tin alloy electrolessly have been unsuccessful because the tin ions poison conventional electroless nickel deposition baths.

In the prior art, tin-nickelphosphorous alloy has been prepared as disclosed in U.S. Pats. Nos. 3,077,421 and 3,077,285 wherein nickel-phosphorous alloy coating is electrolessly deposited upon an iron substate, metallic tin is thereafter plated upon the alloy, and the composite is heated to cause the tin to diifuse into the outer skin of the coating. However, the prior art cited does not teach a method for the simultaneous deposition of Ni and Sn to form an alloy thereof by electroless deposition.

SUMMARY OF THE INVENTION It is an object of this invention to provide methods of depositing Ni-Sn alloy film or Ni-Mo alloy film by electroless deposition.

It is another object of this invention to provide electroless deposition baths for depositing Ni-Sn alloy film or Ni-Mo alloy film.

In accordance with the principles of this invention, an Ni-Sn alloy layer or an Ni-Mo alloy layer is electrolessly deposited from a particularly constituted electroless deposition bath on a suitable substrate such as conventionally activated copper, nickel, iron or other metal substrates, e.g., activated by Pd. The bath is prepared by mixing and diluting stock solutions having therein either sources for nickel ions, tin ions, hypophosphite ions, glycine and tartrate ions; or sources of nickel ions, molybdate ions, glycine, and hypophosphite. Sufiicient hydroxide ions are added to either of the above baths to obtain pH of about 135. Films or layers of either Ni-Sn alloy or Ni-Mo alloy are deposited by immersing a suitable substrate in a bath of this invention for a time sufi'lcient to form a film of desired thickness. The bath is maintained at a temperature of from about 20 C. to about 40 C.

In the practice of an aspect of this invention, an Ni-Sn alloy layer is deposited on a substrate from a particular electroless plating bath in accordance with a method therefor. The bath comprises an aqueous solution having therein about 0.1 mole Ni cations,

Sn(OH) anions in relationship to said Ni cations such that the value of the ratio Sn/Ni is in the range of about 1 to about 4,

about 0.5 mole of glycine,

tartrate in the range of 0.4 to 1.6 moles; and

about 0.2 mole of NaH PO' with the bath having a pH of about 13.5. The method with this bath comprises the steps of immersing a substrate in the bath,

maintaining the bath at temperature in the range of about 20 C. to about 40 C., and thereafter depositing the Ni-Sn alloy layer on the substrate.

In the practice of another aspect of this invention, an Ni-Mo alloy layer is deposited on a substrate from another particular plating bath in accordance with a. method therefor. The bath comprises an aqueous solution having therein about 0.1 mole of Ni cations,

M00 anions in relationship to said Ni cations such that the value of the ratio Mo/Ni is in the range of about 1 to about 5,

about 0.5 mole of glycine, and

about 0.2 mole of NaH PO with the bath having a pH of about 13.5. The method with this bath comprises the steps of immersing a substrate in the bath,

maintaining the bath at temperature in the range of about 20 C. to about 40 C., and thereafter depositing the Ni-Mo alloy layer on the substrate.

The foregoing and other objects, features and advantages of the invention will be apparent from the following more particular description of preferred embodiments of the invention.

GENERAL DESCRIPTION OF THE INVENTION In the preparation of the electroless plating bath of this invention, a stock solution A is prepared by preparing a nickel salt solution containing approximately 0.5 mole of the nickel salt as a source of nickel ions, and containing about 2.5 moles of glycine. For example, 131.5 grams of NiSO -6H O and 187.75 grams of NHgCHgCOOH (glycine) are dissolved in 1 liter of water. A second stock solution B is prepared with a tin salt as a source of tin ions. This solution also contains sodium potassium tartrate or other complexing salts such as sodium potassium citrate. Illustrativcly, the solution contains about 0.5 mole of tin salt and about 2 moles of the tartrate obtained by using 150.3 grams/liter of SnCl -4H O and 460 grams/liter of NaK-tartrate. Sufficient concentrated solution of KOH is added to bring pH of the stock solution B to about 13.5. A third stock solution C is prepared by dissolving from 20.6 grams to 102.5 grams of Na MoO in 1 liter of water for a concentration of from 0.1 mole to 0.5 mole.

The Ni-Sn plating bath is prepared by admixing solution A and solution B and diluting the resultant solution and adding sodium hypophosphite (NaH PO such that the bath contains nickel ions in the range of about 0.1 mole, tin ions from about 0.1 mole to about 0.4 mole, about 0.2 mole of sodium hypophosphite, about 0.5 mole of glycine and from about 0.4 to about 1.6 moles of sodium potassium tartrate. The pH is adjusted so that it is about 13.5.

The Ni-Mo plating bath is prepared by admixing stock solution A and stock solution C and diluting the resultant solution such that it contains about 0.1 mole of Ni, molybdate ions in the range of about 0.1 to about 0.5 moles, and about 0.5 mole of glycine. About 0.2 mole of hypophosphite is added to the resultant solution and KOH is added for pH of about 13.5.

In the practice of this invention, a substrate is immersed in an electroless plating bath of this invention for a time sufiicient to deposit a film of desired thickness. The plating bath should be maintained at a temperature of about 20 C. to about 40 C. Optimally, the plating bath temperature is held between about 30 C. to about 40 C.

While the nickel ion source has been disclosed as nickel sulphate, other nickel salts, e.g., nickel chloride, may also be used as source for nickel ions. Similarly, while SnCl is disclosed as the source for tin ions, other water soluble tin salts may similarly be used as a source for the tin ions. Potassium molybdate may be used instead of sodium molybdate.

EXAMPLES OF THE INVENTION Stock solution A is prepared by dissolving 131.5 g./l. NiSO -6H O (0.5 mole) and 187.75 g./l. NH CH COOH (2.5 moles) in one liter of H 0. An amino acid NH CH OOOH (glycine) is added to complex Ni cations, i.e., Ni++, in the high pH region used for this invention.

Stock solution B is prepared by dissolving 150.3 g./l. SnCl -4H O (0.5 mole) and 460 g./l. NaK-tartrate (0.2 mole) in one liter of H 0.

Concentrated solution of KOH is then added to establish a pH of 13.5. At first Sn(OH) is formed. However, upon further addition of KOH, Sn(OH) anions, i.e., Sn(OH) are formed. In this form tin can be codeposited with nickel without poisoning the electroless plating bath.

Stock solution C is prepared by dissolving from 20.6 grams to 102.5 grams of Na MoO in one liter of water with from 0.1 to 0.5 mole concentration.

Exemplary electroless plating baths for Ni-Sn film of this invention are obtained by adding and diluting stock solutions A and B and the method hereof is practiced as follows:

(a) An aqueous solution is prepared having therein 0.1 mole of Ni, 0.1 mole of Sn, and 0.2 mole of NaH PO with KOH added to give pH=13.6. By immersing an activated Cu substrate in this bath there was deposited Ni-Sn alloy film with 4.6% Sn at 8.5 A./min. when the bath was maintained at temperature of 30 C. An exemplary thickness of the layer was approximately 670 A.

(b) An aqueous solution is prepared having therein 0.1 mole of Ni, 0.4 mole of Sn, and 0.2 mole Of NaI-I PO with KOH added to give pH=l3.5. By immersing an activated Cu substrate in this bath there was deposited Ni-Sn alloy film with 11.9% Sn at 10 A./min. when the bath was maintained at temperature of 35 C. to 38 C.

12;) exemplary thickness of the layer was approximately The electroless plating bath of this invention for Ni-Mo alloy film is obtained by mixing stock solutions A and C and adding NaH Powith the pH adjusted to about 13.5 with KOH. Illustratively, examples of plating baths for NiMo alloy film and the method therefor according to the principles of this invention are as follows:

(1) An aqueous solution is prepared having therein 0.1 mole of NiSO -6H O, 0.5 mole of NH CH COOH, 0.1 mole of N32M0O4, and 0.2 mole of NaH PO- with the pH adjusted to 13.5 with KOH. By immersing an activated Cu substrate in this bath there was plated Ni-Mo alloy film having 1.7% M0 at A./min. when the bath was maintained at temperature of 33 C. An exemplary thickness of the film was about 3200 A.

(2) An aqueous solution is prepared having therein 0.1 mole of NiSO -6H O, 0.5 mole of NH CH COOH, 0.3 mole of Na MoO and 0.2 mole of NaH PO with the pH adjusted to 13.5 with KOH. By immersing an activated Cu substrate in this bath there 'was plated Ni-Mo alloy film having 6.8% M0 at 75 A./min. when the bath was maintained at temperature of 35 C. An exemplary thickness of the film was about 2250 A.

In the preferred embodiments of this invention the pH of the plating bath for Ni-Sn or Ni-Mo should have pH about 13.5. The temperature should be less than 40 C. and greater than 30 C. However, satisfactory results have been obtained in the temperature range of about 20 C. to about 40 C.

Although the hydroxide used for establishing the pH of the plating baths hereof has been stated to be KOH, in accordance with the principles of the invention, other strong bases such as NaOI-I may be used alternatively.

I claim:

1. An electroless plating bath for depositing Ni-Sn alloy layer comprising an aqueous solution having therein:

about 0.1 mole of Ni cations,

Sn(OI-I) anions in relationship to said Ni cations such that value of the ratio Sn/ Ni is in the range of about 1 to about 4,

about 0.5 mole of glycine,

tartrate in the range of 0.4 to 1.6 moles, and

about 0.2 mole of NB-HgPOz,

said bath having a pH of about 13.5.

2. An electroless plating bath for depositing an Ni-Sn alloy layer comprising an aqueous solution having therein:

about 0.1 mole of Ni cations,

about 0.1 mole of Sn(OI-I) anions,

about 0.5 mole of glycine,

about 0.2 mole of NaH 'PO and about 0.4 mole of NaK-tartrate,

said bath having a pH of about 13.5.

3. An electroless plating bath for depositing an Ni-Sn alloy layer comprising an aqueous solution having therein:

about 0.1 mole of Ni cations,

about 0.4 mole of Sn(OH) anions,

about 0.5 mole of glycine,

about 0.2 mole of NaH PO and about 1.6 moles of NaK-tartrate,

said bath having a pH of about 13.5.

4. An electroless plating bath for depositing an Ni-Sn alloy layer comprising an aqueous solution having therein:

about 0.1 mole of NiSOy 6H -O,

about 0.5 mole of NH CH COOH,

about 0.1 mole of Sn(OH) anions,

about 0.4 mole of NaKC H O and about 0.2 mole of Nal-l PO said bath having a pH of about 13.5.

5. An electroless plating bath for depositing an Ni-Sn alloy layer comprising an aqueous solution having therein:

about 0.1 mole of NiSO 6H O,

about 0.5 mole of NH CH COOH,

about 0.4 mole of SnCl -4H O,

about 1.6 moles of NaKC H O and about 0.2 mole of NaH- PO said bath having a pH of about 13.5.

6. A method for electrolessly depositing an Ni-Sn alloy layer comprising the steps of:

immersing a substrate in an electroless plating bath comprising an aqueous solution having therein about 0.1 mole of Ni cations,

Sn(OH) anions in relationship to said Ni cations such that value of the ratio Sn/Ni is in the range of about 1 to about 4,

about 0.5 mole of glycine,

tartrate in the range of 0.4 to 1.6 moles, and

about 0.2 mole of NaH PO said bath having a pH of about 13.5;

maintaining said bath at temperature in the range of about 20 C. to about 40 C.; and thereafter depositing said Ni-Sn alloy layer on said substrate.

7. A method as set forth in claim 6 wherein said Ni-Sn alloy layer is deposited at a rate from about 8.5 A./min. to about A./min.

8. A method as set forth in claim 7 wherein said Ni-Sn alloy layer contains from about 4.6% Sn to about 11.9% Sn, respectively.

9. A method for electrolessly depositing an Ni-Sn alloy layer comprising the steps of immersing a substrate in an electroless plating bath comprising an aqueous solution having therein about 0.1 mole of Ni cations,

about 0.1 mole of Sn(OH) anions,

about 0.5 mole of glycine,

about 0.2 mole of NaH PO and about 0.4 mole of NaK-tartrate,

said bath having a pH of about 13.5;

Cir

til

6 maintaining said bath at temperature in the range of about 30 C. to about 40 C.; and thereafter depositing said Ni-Sn alloy layer on said substrate.

10. A method as set forth in claim 9 wherein said Ni-Sn alloy layer is deposited at a rate of about 8.5 A./min. when said bath is maintained at temperature of about 30 C.

11. A method as set forth in claim 10 wherein said Ni- Sn alloy layer contains about 4.6% Sn.

12. A method for electrolessly depositing an Ni-Sn alloy layer comprising the steps of:

immersing asubstrate in an electroless plating bath comprising an aqueous solution having therein about 0.1 mole of Ni cations,

about 0.4 mole of Sn(O'I-I) anions,

about 0.5 mole of glycine,

about 0.2 mole of NaH PO and about 1.6 moles of NaK-tartrate,

said bath having a pH of about 13.5;

maintaining said bath at temperature range of about 30 C. to about 40 C.; and thereafter depositing said Ni-Sn alloy layer on said substrate.

13. A method as set forth in claim 12 wherein said Ni-Sn alloy layer is deposited at a rate of about 10 A./min. when said bath is maintained at temperature of about 35 C.

14. A method as set forth in claim 13 wherein said 'Ni-Sn alloy layer contains about 11.9% Sn.

References Cited UNITED STATES PATENTS 2,532,283 12/1950 Brenner 106-1 X 3,211,578 10/1965 Gutzeit 1061 X 3,403,035 9/1968 Schneble et al. 1061 3,485,597 12/ 1969 Pearlstein 106-1 X LORENZO B. HAYES, Primary Examiner U.S. Cl. X.R.

ll7-l30 E, R, 240 

